Hi Greg,
Good question.
One distinction is between line breeding in pursuit of gradually improving a particular trait, as you mention, for cleaner colors, for example, on the one hand--and color "morphs" or mutations, on the other hand.
Any trait people breed selectively for has to be passed on genetically, but many of these influences are apparently the result of interaction of multiple (unknown numbers of) genes. Gradually, by continuing to select cleaner and cleaner animals, in this example, one moves toward achieving an animal that's extremely clean. But it's a point on a continuum--as is the case with tangerine and tricolor hondurans, to mention an example existing in wild caught animals. And in the process some will be worse than the norm ("culls"?) and others will be better than the norm and retained for subsequent breedings.
On the other hand, the morphs or mutations you're referring to, and that i work with--amelanistics, hypomelanistics, anerythristics, and the combinations of those traits--are simple recessive traits or the combination of two such traits. Any of these may occur in the wild; when they occur in captivity, that probably proves the gene existed in the wild beforehand. ( Just for background info, the first anerythristic honduran was wild caught, for example, as was the first hypoerythristic pyro pyro.) But more importantly, the trait in question--albinism, for example, will be produced in predictable numbers, and always produced from two homozygous parents. You can't take two animals that are the result of line breeding and which show the desired characteristic, and breed them together and predict that ALL the babies will show the particular characteristic.
Maybe that makes the line-bred animals a bigger challenge, one more deserving of praise, i dunno.
I prefer to think of "designer" as an appropriate term for that tinkering in the lab, LOL. Doing so produces something that perhaps doesn't exist in the wild--that's certainly true of hybrids (ignoring for the purposes of these comments the fact that there may have been a handful of wild-occurring hybrids historically: those animals are notable not because they show something routinely happening in the wild but rather because they're so uncommon and exceptional). And it produces something lacking the predictability of the simple recessive morphs. I think in general usage people sometimes use the "designer" term not only for hybrids but also to refer to line-bred animals that haven't been found in the wild but are perceived by some people as improvements on nature--is the 50-50 cal king perhaps an example? Perhaps someone can post some better examples.
Morphs, recessive color mutations, are traits often, and perhaps almost always, existing in the wild, singularly determined by the actions on a single gene pair, and managed in captivity to increase their numbers. That's important: managed in captivity not to gradually change their appearance to something else, but rather to reproduce more of the particular phenotype (appearance). Yes, we can then breed selectively to produce tangerine albinos, and tricolor albinos, and at that point we're combining the two different breeding practices, i suppose!
Crossing two morphs and managing the pairings of the offspring to produce animals that show the effects of both of two recessive morphs may seem like tinkering with the genetic building blocks, and in a way it is. And unlike the "designer" animals which typically produce a wide range of offspring, only a few of which show the characteristics being sought (those points on a continuum again) any of the morphs, bred as homozygous pairs, produce babies precisely like themselves. And double homozygous pairings would produce babies ALL of which show both traits. This difference from the line-bred animals that are the products of managing many, many genes to shift appearance in a desired direction is an important distinction.
At least that's the way the terms seem to me to have been used. Does that lead us to any useful framework for terminology?
peace
terry
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